Classical techniques for qualitative and quantitative analysis of compositions commonly analyze a sample for the quantity of a particular element present in a sample composition. Exemplary classical analyzing techniques have employed pH measurements, titrations, spectrophotometric and other optical examination processes, electrical processes, and so on, as is well known. Many of the classical analysis techniques disadvantageously have limited resolution. For example, two different compositions, each of which is formed of different component mixtures which provide one or more different sources of a particular element, may under a classical analysis produce a similar result, thus implying that the two compositions are the same or substantially the same. Therefore, total amount of an element, such as nitrogen, or total acidity, etc., may be determined by classical techniques; but resolution between the component parts of a molecule has not been possible using such classical techniques.
Quality control techniques that rely on the aforementioned classical analysis by comparing a sample composition to a reference composition may yield an indication that the sample is acceptable relative to the reference when in fact the sample is unacceptable, for example, being quite different from the intended specifications for the sample. Disadvantages of classical analysis techniques include the limited amount of information that can be obtained within a relatively short time, the narrow range of information obtained, and often lack of sensitivity and ruggedness of the instrumentation. A further disadvantage is the inflexibility of the instrumentation and methods employed in the past to accommodate natural and/or acceptable variations in one or more monitored parameters.
Infrared spectroscopy is a useful tool to identify individual compounds and elements of a sample material or composition. Being able to identify chemical structure, in particular, providing adequate resolution to distinguish between the component parts of a molecule, e.g. to distinguish where a particular carbon hydrogen bond exists rather than just the total amount of carbon or hydrogen, infrared spectroscopy is a good and useful tool for quality control, especially for determining whether a particular material or composition meets expected specifications therefor. Exemplary spectrometer type devices are disclosed in U.S. Pat. Nos. 3,695,764 and 3,902,807. In an exemplary spectrometer a spectrum of information representing characteristics of an examined specimen can be obtained. Such spectrum may include data representing transmittance values of electromagnetic radiation, e.g., light, through the specimen as a function of wavelength, or, more precisely by convention, wave number.
Other background information is presented in the following:
U.S. Pat. No. 4,102,646, issued to Sleeter, relates to a qualitative and quantitative method for analyzing chemical compositions for carbohydrate content using infrared spectroscopy. The analysis is directed toward fructose and dextrose in corn syrups.
U.S. Pat. No. 3,997,786, issued to Lauer, et al, relates to a system for performing on-stream analysis of chemical compositions of a chemical stream in a refinery. The analysis is performed using the principles of spectroscopy.
"Analysis of Cyclopropenoid and Cyclopropanoid Acids in Fats and Oils", by F. C. Magne, The Journal of The American Oil Chemists' Society, Vol. 42, No. 4, pp. 332-336 (Apr., 1965) relates to analysis of cyclopropenoid and cyclopropanoid fatty acid moieties and natural products using infrared spectrophotometry.
"Application of Cryogenic Infrared Spectrometry to the Identification of Petroleum", by P. F. Lynch, S. Y. Tang and C. W. Brown, Analytical Chemistry, Vol. 47, No. 9, pp. 1696-1699 (Aug., 1975) relates to the use of infrared spectrometry in identifying cured and refined petroleum products.